Opening capsules of plastic material having a base or stub fixed on the neck of plastic material of a tube, typically by snap fit, are known in the art, the base comprising a sealing-tight means acting via the interior of the neck, for example a crown inserted by force into the interior of the neck.
Applicant's EP-B-O 192 011 discloses another type of stopper, namely, a cap comprising means for axially force-fitting a tamperproof cover which surmounts the neck of a receptacle. The fitting means are longitudinal scoring radial fins of a plastic material which is harder than that used for the cover.
Applicant have sought to develop an opening capsule adapted to fit such a receptacle which has a tamperproof cover.